1. Field of the Invention
The present invention relates to a latch assembly with adjustable backset. In particular, the present invention relates to a backset-adjustable latch assembly that prevents undesired displacement of a spindle.
2. Description of Related Art
A typical latch Assembly with adjustable backset has been disclosed in, e.g., U.S. Pat. No. 4,615,549. As illustrated in FIGS. 8 through 10 of the drawings which correspond to FIGS. 1 through 3 of U.S. Pat. No. 4,615,549, the dual backset latch includes a lock case (bolt housing) 10, two pulling plates (housing shell halves) 20, a latch bolt 30, a connecting plate (latch operating plate) 40, and front and rear cams 50, 50′. The lock case 10 and the assembling plates 20 together form the main body of the latch assembly. A base portion of the latch bolt 30 extends into the lock case 10. The connecting plate 40 extends through the lock case 10 and between the assembling plates 20, with a front end of the connecting plate 40 being connected to the latch bolt 30 to move therewith. The connecting plate 40 is provided with a pair of rear latch bosses 41 and 42. The assembling plates 20 include two aligned holes 21 and 22. Each cam 50, 50′ has a hub portion 51, 51′, a rectangular spindle slot 52, 52′, and a pair of ears 53, 53′. The cams 50 and 50′ are spaced by the connecting plate 40 and rotatably received in the holes 21 and 22, respectively. When either cam 50, 50′ is turned, the respective ear 53, 53′ presses against the respective latch boss 41, 42, thereby retracting the latch bolt 30 into the lock case 10.
The backset of the front cam 50 is under industry standard 2 and ⅛ inches (or approximately 60 mm) and for the rear cam 50′ 2 and ¾ inches (or approximately 70 mm). When the latch assembly is mounted together with other parts of a door lock to a mounting hole in a door, the installer may selectively extend a spindle (not shown) through either one of the spindle slots 52 and 52′ respectively of the cams 50 and 50′ without adjusting the latch assembly, thereby accomplishing installation.
Although this latch assembly can be used with doors having two standard backset sizes, there are still several drawbacks. Firstly, the spindle holes 52 and 52′ respectively of the cams 50 and 50′ are substantially slanted U-shaped and communicated with each other such that the spindle extending through, e.g., the spindle hole 52 of the cam 50 is apt to slide into the spindle hole 52′ of the cam 50′. The spindle is thus stuck and rotation of either handle (not shown) of the door lock is impossible. Second, the joint area between the two holes 21 and 22 of the respective assembling plate 20 is relatively large such that either cam 50 or 50′ may undesirably enter the incorrect hole 22 or 21. As a result, the cams 50 and 50′ are stuck in the same hole 21 or 22.